This application is the National Stage of International Application No. PCT/JP2017/026040, filed Jul. 19, 2017, which claims the benefit of Japanese Application No. 2016-154748 filed Aug. 5, 2016, the entirety of which is incorporated herein by reference.
Field of the Invention
The disclosure relates to a method and a device that diagnose an abnormality of a feed axis, in a machine such as a machine tool including the feed axis by a ball screw.
Background Art
In a feed axis of a machine tool, a system that transmits rotational motion of a motor to a ball screw for a linear drive is often used. However, in a machine operated for several years, an accuracy failure, an abnormal noise, and the like possibly occur due to a preload loss by abrasion and a damage by entrance of foreign matter, a lubrication failure, or the like. In such a state, a trouble, such as a shape defect, a failure in a pick feed direction, and the like of a workpiece, occurs. Accordingly, it is preferable that machine components such as the ball screw, a bearing, and a linear guide that constitute the feed axis are replaced before deterioration or a damage occurs to generate the trouble.
To know a state of the machine component, it has been proposed that various diagnostic methods such as a method that detects and diagnoses vibration of the ball screw, the bearing, and the linear guide by a vibration sensor, and a method that measures positioning accuracy with a displacement sensor internally disposed. However, in these methods, it is necessary to additionally add a sensor near a site desired to be diagnosed, thus causing a cost increase. Since parts that possibly break down increase, there is also a problem to lead to increase of a breakdown risk.
Therefore, a method that performs the diagnosis using servo information used for control without an additional sensor for diagnosis has been proposed. As a method that determines an abnormality of a reducer, Japanese Patent No. 4112594 proposes a method that performs a frequency analysis on an estimated disturbance value and a torque command in the control to compare spectra in the frequency corresponding to an integral multiple of a rotation frequency of an axis. Japanese Laid-Open Patent Publication No. 2009-68950 proposes a method that, in a machine driven by a motor, performs Fourier transformation on a torque command value, obtains and indicates a spectrum, and focuses on the number of rotations when the motor is rotating and a spectrum in a higher mode caused by the number of rotations to confirm a damage of the machine.